Helena Joyce
Air pollution is a pressing issue that significantly affects climate change and ecosystems, and has a tremendous impact on human health and well-being. It is therefore crucial to measure air pollution to identify its causes and subsequently reduce or regulate them to maintain air quality within legal limits. Air pollution measurement is the process of collecting and measuring the components of air pollution, notably gases and particulates. Modern air pollution measurement is largely automated and carried out using various devices and techniques, such as passive and active devices. Passive devices are simple and low-cost, absorbing ambient air samples for subsequent laboratory analysis. Active devices, on the other hand, are automated or semi-automated and tend to be more complex, employing fans to collect and analyse air samples. Air quality indexes, such as the Air Quality Index (AQI), are also used to communicate the level of air pollution in a given region, with higher numbers indicating worse air quality. These tools help public health officials understand and address the impact of air pollution on human health and the environment.
| Characteristics | Values |
|---|---|
| Air Quality Index (AQI) | The higher the number, the worse the air quality. AQI values at or below 100 are generally considered safe, while values above 100 are deemed unhealthy. |
| Passive Measurement | Diffusion tubes and deposit gauges are examples of passive devices that collect air samples for laboratory analysis. |
| Active Measurement | Automated or semi-automated devices that use fans to collect and analyze air samples immediately or store them for later analysis. |
| Pollutants | PM2.5, PM10, ground-level ozone, nitrogen dioxide, sulfur dioxide, and black carbon are some common pollutants measured. |
| Monitoring Stations | Large, expensive street-side monitoring stations provide continuous data on various urban air pollutants for local authorities. |
| Particulate Measurement | Tapered element oscillating microbalance (TEOM), optical photodetectors, gravimetric analysis, and condensation particle counters are used to measure particulate matter of different sizes. |
| Air Emissions Monitoring | Ambient Air Quality Monitoring and Stationary Source Emissions Monitoring help determine compliance with regulatory requirements and historical standards. |
| Real-time Data | IQAir and UNEP's air pollution exposure calculator provide real-time air quality data and predictions to aid governments in decision-making. |
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What You'll Learn
Air Quality Index (AQI)
The Air Quality Index (AQI) is a numerical system that measures the level of air pollution in a given region. The higher the number, the worse the air quality. The index is split into six different categories, each with a different numerical value, colour and level of concern. An AQI of 50 or below is considered safe, while readings above 100 are deemed unhealthy.
The AQI is based on the measurement of particulate matter (PM2.5 and PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO) emissions. The greater the density of pollutants in the air, the higher the AQI. AQI values reflect air quality management objectives, which are based on the lowest achievable emissions rate, rather than exclusive concern for human health.
The Air Quality Health Index (AQHI) is a scale designed to help understand the impact of air quality on health. It provides a number from 1 to 10+ to indicate the level of health risk associated with local air quality. The AQHI also provides advice on how to improve air quality by proposing behavioural changes to reduce environmental footprints.
AQI readings are obtained from air quality monitors, which are outfitted with sensors designed to detect specific pollutants. Some use lasers to scan particulate matter density in a cubic metre of air, while others rely on satellite imaging to measure energy reflected or emitted by the Earth. There are also passive devices, which are relatively simple and low-cost. They work by soaking up or otherwise passively collecting a sample of the ambient air, which is then analysed in a laboratory.
Air quality databanks process readings from governmental, crowd-sourced, and satellite-derived air quality monitors to produce an aggregated AQI reading. These databases may weigh data differently based on reliability and the type of pollution measured.
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Ground-level monitoring
One commonly used method for ground-level monitoring is the utilisation of low-cost air quality monitors. These sensors can be easily deployed and offer a cost-effective solution for areas lacking government-operated stations or in remote regions. For example, the United Nations Environment Programme (UNEP) has supported the installation of 48 low-cost sensors across Kenya, Costa Rica, Ethiopia, and Uganda. These sensors contribute to the growing global network of air quality monitors, providing real-time data on pollution levels.
Mobile monitoring platforms also play a significant role in ground-level pollution measurement. These include on-road vehicles, trains, trams, bicycles, and even manned and unmanned aircraft. By equipping these mobile platforms with regulatory and research-grade instruments, high-quality data can be obtained. This allows for the study of human exposure to air pollutants, transport phenomena, and chemical transformations. Additionally, mobile platforms can be used in combination with ground-based measurements to maximise the advantages of each platform and improve spatial coverage.
To address the challenges of ground-level monitoring, advancements in technology have led to the development of satellite-driven tools as a supplementary method. Satellite observations of airborne particles, combined with models of atmospheric chemistry, provide a global perspective on air pollution. For instance, the Global Burden of Disease study utilised satellite data, ground-level measurements, and atmospheric models to offer one of the first comprehensive views of exposure to outdoor PM2.5 pollution and its associated health impacts.
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Satellite technology
NASA's Tropospheric Emissions: Monitoring of Pollution (TEMPO) satellite mission is an example of a satellite network that monitors air pollution in near real-time. TEMPO's sensors detect tiny differences in the light reflected when sunlight strikes molecules in the atmosphere and gets absorbed at specific wavelengths. It can track ozone, nitrogen dioxide, sulfur dioxide, bromine, formaldehyde, and tiny airborne particles called aerosols. TEMPO measures air pollutants in the atmosphere, including ozone, nitrogen dioxide, and formaldehyde, every hour across greater North America down to a neighbourhood scale.
The GEMS satellite has delivered insights into the daily rhythms of nitrogen dioxide pollution across much of Asia. It has also tracked dust storms from northern China and sulfur dioxide from volcanic eruptions.
Another tool for accessing, visualizing, and analyzing NASA satellite data is Giovanni. With Giovanni, aerosol optical depth measurements for a region can be correlated with EPA ground measurements of particles to determine whether the aerosols the satellite measured were high in the atmosphere or close to the ground.
Satellite data of atmospheric pollutants are becoming more widely used in the decision-making and environmental management activities of public, private, and non-profit organizations. They are used for estimating emissions, tracking pollutant plumes, supporting air quality forecasting, providing evidence for "exceptional event" declarations, monitoring regional long-term trends, and evaluating air quality model output.
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Biomonitors
Biomonitoring involves using organisms to assess environmental contamination of the air, water, or soil. It can be done in two ways: qualitatively, by observing and noting changes in organisms, or quantitatively, by measuring the accumulation of chemicals in their tissues.
Biomonitoring can be used to detect the presence and severity of air pollution. For example, the presence of the lichen *Lecanora conizaeoides* indicates poor air quality, while reductions in lichen chlorophyll content or diversity indicate the presence and severity of air pollution. Plants can also be used to determine the type of air pollutant, as different pollutants cause different damage symptoms. In addition, the extent of damage to plants and the duration of exposure can be used to estimate the concentration and mass of the pollutant.
In addition to plants, animals can also be used as bioindicators. For example, canaries were historically used in coal mines to detect the presence of carbon monoxide and methane gas. Their small lung capacity and unidirectional lung ventilation system made them more vulnerable to these gases than humans, and their acute sensitivity served as a warning of unsafe conditions.
Biomonitoring can also be used to detect pollutants in water. For example, native mosses can be used to monitor fluorine levels and associated temporal variations near an aluminium smelter. Similarly, mosses have been used to monitor the atmospheric deposition of persistent organic pollutants (POPs) and heavy metals.
Human biomonitoring involves analysing the levels of pollutants in human bodily substances such as blood, urine, exhaled air, hair, nails, feces, semen, breast milk, or saliva. This can help to assess the potential health risks associated with exposure to pollutants. For example, breast milk can be used to measure lipophilic (fat-loving) toxic compounds during lactation, which is relevant for breastfeeding children.
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Health impacts
Air pollution is a major threat to global health and prosperity, causing more than 6.5 million deaths each year worldwide. It is caused by a combination of human-made and natural sources, including vehicle emissions, fuel oils, natural gas, manufacturing by-products, power generation, and fumes from chemical plants. The health impacts of air pollution are extensive and far-reaching, affecting people from all socio-economic backgrounds.
One of the most significant health impacts of air pollution is its contribution to respiratory problems. Fine particulate matter (PM2.5), a common air pollutant, can be inhaled deeply into the lungs, causing serious health issues such as oxidative stress, inflammation, and immunosuppression in cells throughout the body. This can lead to respiratory diseases such as chronic obstructive pulmonary disease, trachea, bronchus, and lung cancers, aggravated asthma, and lower respiratory infections. Older people, children, and those with pre-existing health conditions, such as heart or lung disease, are more vulnerable to the health impacts of air pollution.
Air pollution has also been linked to an increased risk of cardiovascular disease, including coronary heart disease, heart attacks, and heart surgery. Studies have found that exposure to PM2.5, particularly from coal-powered plants, is associated with a higher mortality risk. Additionally, air pollution has been implicated in the development of systemic inflammation, Alzheimer's disease, dementia, and cancer. The International Agency for Research on Cancer has classified air pollution as a leading cause of cancer, specifically lung cancer.
Indoor pollution, generated by household combustion of fuels, can also have significant health impacts. High concentrations of indoor air pollutants can cause both short-term and long-term health effects, particularly in susceptible populations such as the elderly, children, and people with pre-existing health conditions. Maternal exposure to indoor air pollution has been associated with adverse birth outcomes, including low birth weight, pre-term birth, and small gestational age births.
Furthermore, air pollution has been linked to an increased risk of diabetes, obesity, cognitive impairment, and neurological diseases. The World Health Organization (WHO) has identified links between air pollution exposure and the development of type 2 diabetes, obesity, and neurological disorders. Overall, the health impacts of air pollution are extensive and severe, underscoring the importance of implementing effective policies and measures to improve air quality and protect public health.
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Frequently asked questions
The Air Quality Index (AQI) is a scale that runs from zero to 500, with higher numbers indicating worse air quality and a greater health concern. An AQI of 50 or below is generally considered safe, while readings above 100 are deemed unhealthy. The AQI is divided into six colour-coded categories, each with a specific level of health concern.
Passive devices are relatively simple and low-cost. They collect samples of ambient air, which are then analysed in a laboratory. One of the most common forms of passive measurement is the diffusion tube, which absorbs specific pollutant gases. Active devices are automated or semi-automated and tend to be more complex. They use fans to suck in the air, filter it, and either analyse it immediately or store it for later analysis.
In public spaces, static air quality monitors are often used to provide immediate feedback on local air quality. For example, in Poland, EkoSłupek air monitors measure a range of pollutants and have lamps that change colour to indicate the healthiness of the air. There are also large, expensive, street-side monitoring stations that sample urban air for local authorities, such as the London Air Quality Network.
